The present invention relates to a differential impulse conveyor for moving goods along the conveyor tray. More particularly, this invention relates to an improved drive mechanism for powering a differential impulse conveyor in a manner that reduces undesirable vibration and mechanical knock in the drive mechanism and the conveyor tray.
A differential impulse conveyor includes a generally elongate horizontal or slightly inclined tray or pan having a planar surface for transporting goods thereon. The tray is moved slowly forward to convey the goods with respect to the tray and is then pulled rearward at a high return speed so that the goods slide along the tray, thereby effectively transporting the goods along the conveyor tray. Differential impulse conveyors, which are sometimes referred to as linear motion conveyors, are operationally distinguishable from other types of conveyors, such as reciprocating conveyors, shuffle conveyors, vibrating conveyors, or shaker conveyors. A significant advantage of differential impulse conveyors is that goods may be transported along the unitary tray (no moving tray parts) in a manner that does not tend to damage fragile goods. Differential impulse conveyors have thus been preferred in many applications, such as food handling, when conveyor cleanliness, low noise, and minimal product damage are desired.
The drive mechanism of a differential impulse conveyor generates repeated acceleration and deceleration of the tray. Inherently the forward acceleration is lower than the rearward acceleration so that goods slide along the tray substantially only when the tray is pulled rearward at a high return speed. One type of prior art mechanism for driving a differential impulse conveyor includes a plurality of flywheels suspended from the conveyor tray such that the momentum of the rotating flywheels achieves the desired slow forward speed and high return speed for the conveyor tray. This flywheel drive mechanism is costly and cannot be easily optimized to adjust the ratio of the forward speed and return speed to achieve the desired product speed along the conveyor tray.
An improved differential conveyor is disclosed in U.S. Pat. No. 5,351,807 (xe2x80x2807 patent). The drive mechanism of this conveyor employs an angled universal joint in combination with a 1:2 speed enhancer to achieve one half cycle rotation of a drive shaft at a slow speed followed by one half cycle rotation of the drive shaft at a high speed. A crank interconnects the drive shaft and the tray to achieve the desired conveyor movement. The angle of the universal joint and the speed of the motor may be adjusted to maximize product travel along the conveyor tray. A counterweight is also driven by the drive shaft to move 180xc2x0 out of phase with the conveyor tray movement, thereby substantially reducing undesirable conveyor vibration and mechanical knock in the drive system. A hydraulic fluid pump may also be driven by the drive shaft to serve a dampening function and further reduce knock in the drive mechanism.
Although the techniques disclosed in the xe2x80x2807 patent have significantly advanced the acceptance of differential impulse conveyors, improvements to further reduce or eliminate mechanical knock in the drive system are desired. Hydraulic dampening is not preferred for many food processing applications, wherein hydraulic fluid is avoided due to contamination and safety concerns. By further reducing mechanical knock in the drive mechanism, the size and thus the cost of conveyor drive components may be reduced without adversely affecting the useful life of the conveyor. In some applications, it may be desirable to drive the conveyor with a motor rotating a shaft at a speed much higher than the speed desired for the varying half cycle drive shaft. Optimization of the drive mechanism will further enhance acceptance of differential impulse conveyors as a practical alternative to reciprocating conveyors, shuffle conveyors, vibrating conveyors, and shaker conveyors.
Another problem with conveyors designed to move goods along a substantially horizontal surface of a tray by either differential impulse or vibration techniques concerns the difficulty with moving the pan so that the area beneath the tray may be easily cleaned. While the drive mechanism is typically detachable from the conveyor tray, a good deal of time and expertise is required to detach the drive mechanism from the tray, move the tray away from the drive mechanism for cleaning, then reattach the drive mechanism to the tray. Also, conveyor pans supplying goods to scales or weighers require precise positioning of the pan for optimal feeding of the scale or weigher. In order to reduce the time required for cleaning the area beneath the tray, the entire conveyor including the tray and drive mechanism have been movably supported on rails. The conveyor assembly weighing in excess of several thousand pounds may thus be rolled out along the rails for cleaning, then rolled back into its proper position with respect to the scale. Considerable expense is thus expended to move the conveyor for cleaning, then to properly reposition the conveyor with respect to the scale.
The disadvantages of the prior art are overcome by the present invention. An improved differential impulse conveyor and the drive mechanism for a differential impulse conveyor which desirably reduces mechanical knock are hereinafter disclosed. The drive mechanism optionally allows the motor shaft to be rotated at a speed much greater than the drive shaft, thereby reducing the cost of the conveyor drive mechanism.
The differential impulse conveyor includes a tray movable in a forward direction at a first speed and in a backward direction at a second speed greater than the first speed to move goods along the tray in the forward direction. In one embodiment of the invention, the conveyor drive mechanism includes a universal joint to convert substantially constant rotational motion of the motor shaft into varying rotational speed of a drive shaft, such that the drive shaft rotates at a slow speed during one half cycle of rotation and then a fast speed during the next half cycle of rotation. A crank is connected between the drive shaft and the tray to push the conveyor slowly forward and then pull the conveyor quickly backward. To reduce overrun knocking in the conveyor drive mechanism, two counterweights are provided, each movable relative to the tray. The tray and each counterweight may be pivotally supported from a base by pairs of generally vertical support arms. A corresponding plurality of counterweight cranks interconnect each counterweight with the drive shaft for initiating forward movement of the counterweights at an offset angular position of 120xc2x0 with respect to initial forward movement of the tray.
In another embodiment of the invention, an electronic controller is provided for controlling the rotational speed of the motor shaft to cause the motor shaft to rotate at a first speed during a first rotational period and at a second speed greater than the first speed during a second rotational period of a duration equal to the first period. The controller and motor may be combined to be functionally and operationally equivalent to a programmed servo motor. By directly controlling the rotational speed of the motor shaft, the universal joint is not required. The motor shaft may be connected directly to a tray crank for moving the tray and to one or more counterweight cranks each interconnected with a respective counterweight. Alternatively, a torque multiplier or speed reducer may be provided between the motor shaft and the drive shaft for rotating the tray crank and the one or more counterweight cranks, thereby benefiting from a higher rpm and lower cost motor. In this latter embodiment, the torque multiplier preferably is a wormgear mechanism that has substantially zero backlash to accommodate the overrunning load.
A connector mechanism is provided for supporting the pan between pairs of support arms each pivotally connected to a base. When the conveyor is not powered, the connector mechanism may be released so that the pan may be slid laterally with respect to the support arms, thereby allowing for easy cleaning of the entire area normally beneath the tray. The tray may then be slid back into its original position and reconnected to the support arms. The connector mechanism further allows the lateral positioning of the pan to be easily adjusted with respect to the support arms and thus the conveyor base for desirably positioning the tray laterally with respect to a scale.
It is an object of the present invention to provide an improved differential impulse conveyor which minimizes mechanical knock due to overrun loads in the drive mechanism. It is a related object of the invention to provide a differential impulse conveyor that is relatively inexpensive and is not susceptible to high maintenance and repair costs.
A particular feature of the invention is the utilization of the plurality of counterweights, and preferably two counterweights, each driven by the drive shaft that drives the conveyor tray. A tray crank interconnects the drive shaft with the tray to initiate forward movement of the tray at a selected angular position of the drive shaft. Each counterweight is interconnected with the drive shaft by a counterweight crank that initiates forward movement of each counterweight at a preselected angular position of the drive shaft with respect to the selected angular position for initiating forward movement of the tray. Each counterweight preferably has a selected weight so that the maximum momentum of each counterweight is substantially equal to the maximum momentum of the tray.
It is another feature of the invention that a controller is utilized to control the rotational speed of the motor shaft to cause the motor shaft to rotate at a first speed during a first rotational period and at a second speed greater than the first speed during a second rotational period. The tray crank and one or more counterweight cranks may be directly connected to the varying speed motor shaft, or a torque converter (speed reducer) may be utilized between the varying speed motor shaft and the varying speed drive shaft for interconnection with both the tray crank and the one or more counterweight cranks. It is a further feature of the invention that the wormgear mechanism is utilized as the torque converter between the varying speed motor shaft and the drive shaft to minimize backlash and overrun loads on the drive shaft.
A further feature of the invention is that the drive mechanism for the differential impulse conveyor may be utilized to drive both a substantially horizontal tray, an inclined tray having a planar tray surface, or a vertically spiraling conveyor tray. Yet another feature of the invention is that the drive mechanism for the differential impulse conveyor may be easily modified to alter the speed at which goods are moved along the conveyor tray.
Still another feature of the invention is that an eccentric pulley rotated by the drive motor and a flexible belt interconnecting the eccentric pulley and the drive shaft may be used to achieve the desired varying speed of the drive shaft. The drive shaft rotates an eccentrically mounted tray crank which is connected to the tray, and one or more eccentrically mounted counterweight cranks each driving a respective counterweight. A make-up pulley or other eccentric compensator acts on the flexible belt to maintain the predetermined relationship between rotation of the drive shaft and the motor shaft.
Yet another feature of the invention is a connector mechanism for supporting a conveyor tray between pairs of spaced apart support arms each pivotally connected to a base. The connector mechanism allows the pan to be laterally moved out of position while still being supported on the support arms, so that the area beneath the tray may be easily cleaned. The connector mechanism also facilitates inspection and periodic adjustment or service of the conveyor drive mechanism. After cleaning, the tray may be easily slid back into its original position, and if necessary the lateral position of the tray may be easily adjusted.
It is an advantage of the present invention that the drive mechanism for the differential impulse conveyor is relatively simple and thus inexpensive to manufacture and easy to maintain. The cost of a drive mechanism is significantly reduced by providing relatively few drive mechanism components . If a plurality of counterweights are used to substantially reduce or eliminate knocking, the conveyor may be reliably driven by a conventional motor, a universal joint, and a 1:2 speed increase mechanism.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.